Twelve-year-old Katherine Bateson believes in a logical explanation for everything. But even she can't make sense of the strange goings-on at Rookskill Castle, the drafty old Scottish castle-turned-school where she and her siblings have been sent to escape the London Blitz. What's making those mechanical shrieks at night? Why do the castle's walls seem to have a mind of their own? And who are the silent children who seem to haunt Rookskill's grounds? Kat believes Lady Eleanor, who rules the castle, is harboring a Nazi spy. But when her classmates begin to vanish, one by one, Kat must face the truth about what the castle actually harbors--and what Lady Eleanor is--before it's too late.